Non-aqueous electrolyte secondary batteries have a high capacity and a high energy density and can be easily made compact and lightweight, and for this reason, are widely used as a power source for electronic equipment, electric equipment, transportation equipment, machining equipment, power storage equipment, and the like. A typical non-aqueous electrolyte secondary battery is a lithium ion secondary battery including a positive electrode including a lithium-cobalt composite oxide, a negative electrode including graphite, and a separator.
Another known negative electrode active material other than graphite is an alloy-formable active material such as silicon, tin, and an oxide or alloy of silicon or tin. The alloy-formable active material absorbs lithium by alloying with lithium and reversibly absorbs and desorbs lithium. The alloy-formable active material has a high discharge capacity. For example, the theoretical discharge capacity of silicon is about 11 times as large as the theoretical discharge capacity of graphite. Therefore, a non-aqueous electrolyte secondary battery using an alloy-formable active material as the negative electrode active material has a high capacity.
The non-aqueous electrolyte secondary battery using an alloy-formable active material as the negative electrode active material (hereinafter also referred to as the “alloy-type secondary battery”) exhibits excellent performance at the beginning of use. However, the problem is that the battery performance deteriorates over time because the electrode deterioration, battery deformation, and the like occur with the increase in the number of charge/discharge cycles. In order to solve this problem, the following proposals have been suggested.
Patent Literature 1 discloses a negative electrode for a non-aqueous electrolyte secondary battery, in which a polymer film layer formed of a polymer support and a cross-linker monomer is provided on the surface of the negative electrode active material layer including lithium alloy particles.
Patent Literature 2 discloses a negative electrode for a non-aqueous electrolyte secondary battery, in which an oxide film composed of an oxide of metal selected from the group consisting of silicon, germanium, and tin is formed on a region of the surface of a negative electrode active material particle being supported on the current collector and containing silicon or tin, the region being brought into contact with the electrolyte.